Buy or Wait is always tough with regards to apple kit, imo.
We bought a load of stuff last year in October (i7 Radeon Mac Mini, 32GB Wifi iPad2, Apple TV 2, 3TB Time Capsule....)
If new stuff gets announced and its loads better, you can always be happy in the knowledge that if you looked after your kit and kept the boxes, you can always make good money selling them and pay a minimal cost to upgrade.
I won't bother upgrading to a new Apple TV as my bedroom TV is only 720p, unless the features go far beyond that.
Would we upgrade the iPad? maybe. We use it A LOT, and decent improvements could be nice to have.